It is only in the past decade that digital switching apparatus have become widely available in the form of central office and private branch exchanges. During this period, regulatory agencies in various countries have become concerned with such apparatus as a source of undesirable electromagnetic interference (EMI), particularly at frequencies of about 30 MHz, and higher. The trend toward higher control processor clock frequencies and more densely packaged circuitry has only exacerbated this problem. A typical approach to reducing the EMI radiated by such apparatus has been to encase the apparatus in a metal cabinet intended to function as an electromagnetic shield or container. However the multitude of telecommunciations lines and trunks which orginate within the apparatus and pass through openings in the shield tend to act as effective radiating antennas which substantially nullified the intended effect of the shield. It has since been observed that the amount of lead length of the lines and trunks inside the shield has a direct effect upon propagation of EMI. It was subsequently realized that capacitive feedthrough connectors fixed in the shield provide an input/output interconnect means which is effective in reducing EMI radiation to tolerable levels. For example in the case of tip and ring conductors of an analog telephone line being terminated in a typical DMS type telephone facility, a connector feedthrough capacitance of between 1000 and 15000 picofarads has been found to be quite helpful. However, in the case of a digital trunk being operated in the T1 standard format of about 1.5 MHz, a little more than 300 pf is tolerable before the form of the TDM binary signal bit stream carried by the trunk becomes unacceptably distorted. Consequently, digital trunks are each a greater contributor to the radiated EMI than are the analog lines. Fortunately, there are usually far fewer digital trunks than there are analog lines and the detrimental increase in EMI is small.
Recently, proposed switching machines are characterized by more tightly packaged electronic circuitry which operates at greater speeds. Furthermore, such machines provide among other features fully digitized twisted pair communication lines. Some of these communication lines are intended to operate at binary bit frequencies of up to almost 3 MHz. In such a machine the problem of meeting acceptable EMI limits is greatly magnified by the abundance of the digital signal twisted pair communication lines, and by the fact that from an operating viewpoint it is most preferable that the capacitance of the associated feedthrough connectors be substantially reduced.